全項目入力で有効化される送信ボタン

<form class="d04-11-10-form" novalidate>
          <input type="text" class="d04-11-10-in" placeholder="お名前" aria-label="お名前">
          <input type="email" class="d04-11-10-in" placeholder="メールアドレス" aria-label="メールアドレス">
          <textarea class="d04-11-10-in d04-11-10-ta" placeholder="お問い合わせ内容" rows="2" aria-label="お問い合わせ内容"></textarea>
          <button type="submit" class="d04-11-10-btn" disabled>送信する</button>
          <p class="d04-11-10-ok">送信しました。ありがとうございます!</p>
        </form>

.d04-11-10-form{width:min(260px,100%);display:flex;flex-direction:column;gap:8px}
        .d04-11-10-in{width:100%;padding:10px 12px;font-size:13px;font-family:inherit;border:2px solid #d5d9e0;border-radius:8px;outline:none;background:#fff;transition:border-color .25s;resize:none}
        .d04-11-10-in:focus{border-color:#4a6cf7}
        .d04-11-10-btn{margin-top:4px;padding:11px;font-size:14px;font-weight:700;color:#fff;background:#c3c9d4;border:none;border-radius:8px;cursor:not-allowed;transition:background .25s}
        .d04-11-10-btn:not(:disabled){background:#4a6cf7;cursor:pointer}
        .d04-11-10-btn:not(:disabled):hover{background:#3a58d6}
        .d04-11-10-ok{display:none;margin:0;padding:9px;text-align:center;font-size:12px;font-weight:700;color:#1c7c4e;background:#e2f6ec;border-radius:8px}
        .d04-11-10-form.is-success .d04-11-10-ok{display:block}
        .d04-11-10-form.is-success .d04-11-10-btn{display:none}

(function(){
        var form=document.querySelector('.d04-11-10-form');
        if(!form)return;
        var inputs=Array.prototype.slice.call(form.querySelectorAll('.d04-11-10-in'));
        var btn=form.querySelector('.d04-11-10-btn');
        function checkAll(){
          var filled=inputs.every(function(el){return el.value.trim()!=='';});
          btn.disabled=!filled;
        }
        inputs.forEach(function(el){el.addEventListener('input',checkAll);});
        form.addEventListener('submit',function(e){
          e.preventDefault();
          if(btn.disabled)return;
          form.classList.add('is-success');
        });
      })();